Cayin RU9 Portable Nutube USB DAC/Head-Amp
We think the RU9's killer feature is MagSafe compatibility, letting it attach directly to a compatible phone, and the choice between solid state and a subtle, non-goopy tube mode makes it a nice way to sweeten headphones with strong attack. The noise floor is impressively low, though we wouldn't call it a powerhouse, if you want desktop levels of power, that's what the C92 is for, at the cost of size and weight.
Cayin RU9, Gen5 Vacuum Tube Circuit for Portable Audio (2024)
With the RU9, Cayin has entered the fifth generation of Nutube application. The Gen5 Nutube Timbre circuit features a refined three-stage amplification architecture. Cayin engineers have meticulously designed and fine-tuned the negative feedback (NFB) loops to deliver distinct Nutube 6P1 vacuum tube timbres, while also integrating the Dual Tube Timbre feature first introduced in Gen3—offering users a seamless blend of dual tube warmth and solid-state precision.
Switchable Output: Classic / Modern / Solid State
Both 3.5mm and 4.4mm PO/LO outputs support two switchable Tube Timbres and a Solid-State Timbre.
- Classic Tube Timbre: No large-loop NFB; each stage operates independently through local feedback, and the overall gain determined by the cumulative gain of each stage. Distortion characteristics closely resemble classic tube amplifier, resulting in a higher THD value. The sound signature exhibit a classic vacuum tube amplifier, with relatively more thermal noise and a richer presentation.
- Modern Tube Timbre: A large-loop NFB circuit will determine the total gain. By incorporating NFB over multiple amplification stages, the THD will be reduced significantly.
The harmonic distortion characteristics and sound signature lean more towards a modern style, with greatly reduced thermal noise and a slightly cleaner tube sound. - Solid-state Timbre: Built with op-amps and precision-tuned peripheral circuits. Delivers accurate resolution, fast dynamics, and neutral tonality.
Anti-Vibration System
Custom-designed anti-vibration module for the Nutube tube, featuring an FPC flexible PCB, a custom silicone damping sleeve, and a pin suspension system. Engineered to eliminate microphonic interference.
Hyper Mode
Hyper Mode is automatically activated under DC Mode.
It further increases the amplifier's quiescent current and operating voltage, offering greater clarity, expansive soundstage, and punchier dynamics.
Triple Power Modes
The Cayin RU9 offers three flexible power modes to suit a wide range of usage scenarios. Whether you're on the go or chasing peak performance, choose between:
- When USB IN is connected: Dongle Mode - ideal for compact "dongle-style" use.
- When POWER is connected:
Battery Mode - system runs primarily on USB power, with internal battery providing backup support.
DC Mode - full external power delivery with direct routing to the amplifier circuit, automatically activates Hyper Mode for maximum output.
Supports QC3.0 and PD2.0 fast charging protocols.
Thoughtful Design
The Cayin RU9 features a magnetic attachment system, seamlessly attaching to compatible smartphones and tablets. A magnetic adapter ring and a custom magnetic leather case is included, handcrafted with precise cutouts.
Also included is an L-shaped USB interconnect cable. Shielded with a braided design for reduced signal loss.
The RU9 offers three timbre modes you can switch between on the fly. Classic Tube delivers the rich, dense, warm sound traditional tube fans love. Modern Tube is a cleaner, slightly brighter take that keeps the smoothness of tubes while adding a touch more refinement. Solid State bypasses the tube entirely, using op-amps for a neutral, fast, and accurate sound signature. All three modes are available from both the 3.5mm and 4.4mm outputs.
Hyper Mode is a special high-performance setting that becomes available when the RU9 is connected to an external DC power supply. It increases the amplifier's operating current and voltage, pushing balanced output up to 1000mW per channel at 32Ω — enough to drive demanding full-sized headphones with authority. It does generate more heat than normal operation, so it's best used at a desk rather than on the go. For most IEMs and portable headphones, standard battery or USB power will be more than sufficient.
Via USB, the RU9 decodes PCM up to 32-bit/768kHz and native DSD up to DSD512, handled by the XMOS XU316 16-core processor and dual AK4493SEQ DAC chips running in mono mode. Over Bluetooth 5.1 it supports LDAC, aptX HD, aptX Low Latency, AAC, and SBC. The S/PDIF input (shared with the 3.5mm port) supports up to 24-bit/192kHz PCM for connecting CD transports or external sources.
The built-in 2000mAh battery provides up to 4.7 hours of playback, though real-world use with the balanced output and tube modes at higher volumes is typically closer to 3–4 hours. Yes, you can listen continuously while charging — the RU9 supports QC and PD fast charging via its dedicated power USB-C port, separate from the data port. You can also run it in USB power mode directly from your phone or laptop, which bypasses the battery entirely and keeps it from draining.
Yes — the RU9 is unusually powerful for its size. The balanced 4.4mm output delivers 1000mW per channel at 32Ω and 1170mW at 16Ω in Hyper Mode, while the single-ended 3.5mm output puts out 420mW at 32Ω. This is more than enough to drive demanding full-sized planar magnetic and dynamic headphones with high impedance loads. For the most power-hungry headphones, using Hyper Mode with an external DC supply will give the best results.
Frequently Asked Questions
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Further optimised reference class in wired headphones
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Open, circum-aural dynamic stereo headphones
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Enhanced sound reproduction achieved through absorber technology
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Additional cable with balanced 4.4mm connector
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High-class matte black metal parts
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Natural hearing experience - realistic and natural sound field with minimal resonance
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Biggest transducers ever used in headphones including new innovative dynamic transducer design
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Uncovered earcups for enhanced acoustics
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Handcrafted ear pads, made of high-quality microfiber fabric
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Metal headband with an inner damping element
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Specially tuned balanced, impedance matching cable with low capacitance
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Special high precision headphone connectors
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2 year warranty
- Cayin RU9
- USB-C to USB-A adapter
- USB-C to USB-C cable (short)
- Pleather cover with magsafe compatibility
- Documentation
The RU9 offers three timbre modes you can switch between on the fly. Classic Tube delivers the rich, dense, warm sound traditional tube fans love. Modern Tube is a cleaner, slightly brighter take that keeps the smoothness of tubes while adding a touch more refinement. Solid State bypasses the tube entirely, using op-amps for a neutral, fast, and accurate sound signature. All three modes are available from both the 3.5mm and 4.4mm outputs.
Hyper Mode is a special high-performance setting that becomes available when the RU9 is connected to an external DC power supply. It increases the amplifier's operating current and voltage, pushing balanced output up to 1000mW per channel at 32Ω — enough to drive demanding full-sized headphones with authority. It does generate more heat than normal operation, so it's best used at a desk rather than on the go. For most IEMs and portable headphones, standard battery or USB power will be more than sufficient.
Via USB, the RU9 decodes PCM up to 32-bit/768kHz and native DSD up to DSD512, handled by the XMOS XU316 16-core processor and dual AK4493SEQ DAC chips running in mono mode. Over Bluetooth 5.1 it supports LDAC, aptX HD, aptX Low Latency, AAC, and SBC. The S/PDIF input (shared with the 3.5mm port) supports up to 24-bit/192kHz PCM for connecting CD transports or external sources.
The built-in 2000mAh battery provides up to 4.7 hours of playback, though real-world use with the balanced output and tube modes at higher volumes is typically closer to 3–4 hours. Yes, you can listen continuously while charging — the RU9 supports QC and PD fast charging via its dedicated power USB-C port, separate from the data port. You can also run it in USB power mode directly from your phone or laptop, which bypasses the battery entirely and keeps it from draining.
Yes — the RU9 is unusually powerful for its size. The balanced 4.4mm output delivers 1000mW per channel at 32Ω and 1170mW at 16Ω in Hyper Mode, while the single-ended 3.5mm output puts out 420mW at 32Ω. This is more than enough to drive demanding full-sized planar magnetic and dynamic headphones with high impedance loads. For the most power-hungry headphones, using Hyper Mode with an external DC supply will give the best results.
Frequently Asked Questions
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Cayin RU9 Portable Nutube USB DAC/Head-Amp
The fifth generation of Cayin's Nutube implementation
The fifth generation of Cayin's Nutube implementation
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Found a lower price?
Please complete the form below.
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